Fuel cells are devices that directly convert chemical energy of reactants, i.e., fuel and oxidant, into direct current (DC) electricity. For an increasing number of applications, fuel cells are more efficient than conventional power generation, such as the combustion of fossil fuels, as well as portable power storage, such as lithium-ion batteries. In particular, one use of fuel cells is as a mobile power source for portable or mobile consumer electronic devices, such as cell phones, smart phones, personal digital assistants, personal gaming devices, global positioning devices, rechargeable batteries, computer tablets, laptop computers, etc.
Known fuel cells include alkali fuel cells, polymer electrolyte fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, and enzyme fuel cells. Fuel cells generally run on hydrogen (H2) fuel, and they can also consume non pure hydrogen fuel. Non pure hydrogen fuel cells include direct oxidation fuel cells, such as direct methanol fuel cells (DMFC), which use methanol, or solid oxide fuel cells (SOFC), which use hydrocarbon at high temperature. Hydrogen fuel can be stored in compressed form or within compounds, such as alcohols or hydrocarbons or other hydrogen containing materials, that can be reformed or converted into hydrogen fuel and byproducts. Hydrogen can also be stored in chemical hydrides, such as sodium borohydride (NaBH4), that react with water or an alcohol to produce hydrogen and byproducts. Hydrogen can also be adsorbed or absorbed in metal hydrides, such as lanthanum pentanickel (LaNi5), at a first pressure and temperature and released to a fuel cell at a second pressure and temperature. Hydrogen can also be released via thermolysis reaction of a metal hydride, such as magnesium hydride (MgH2).
Most low temperature hydrogen fuel cells have a proton exchange membrane, or polymer electrolyte membrane (PEM), which allows the hydrogen's protons to pass through, but forces the electrons to pass through an external circuit, which advantageously can be a smart phone, a personal digital assistant (PDA), a computer, a power tool, or any device that uses electron flow or electrical current. The fuel cell reaction can be represented as follows:
Half-reaction at the anode of the fuel cell:H2→2H++2e−;
Half-reaction at the cathode of the fuel cell:2(2H++2e−)+O2→2H2O.
Generally, the PEM is made from a proton exchange polymer that acts as the electrolyte, such as Nafion® available from DuPont, which is a perfluorinated sulfonic acid polymer, or other suitable membranes. The anode is typically made from a Teflonized carbon paper support with a thin layer of catalyst, such as platinum-ruthenium, deposited thereon. The cathode is typically a gas diffusion electrode in which platinum particles are bonded to one side of the membrane.
The patent and scientific literatures disclose few gas or hydrogen gas generation systems that automatically separate the catalyst from the reactants when a predetermined pressure is reached. However, there remains a need for additional designs.